The invention relates to a differential gearing for the distribution of torque from an input shaft to two driven shafts, having a first gearing component connected to the input shaft, and which is in permanent rotatable connection with two further gearing components connected respectively to the two driven shafts, said gearing also having a hydraulic self-locking mechanism comprising pinions, which are connected to the first gearing component, and which are tightly contained within a housing and work in conjunction with the second and/or third gearing components as a geared pump having throttling clearances. Such a differential gearing is used in motor vehicles, for example, to transmit the driving torque to the two wheels of a driving axle or also in a drive line between several driven axles.
The invention proceeds from a differential gearing with a hydrostatic self-locking mechanism known from German Patent Document No. 35 42 184. This known design involves a differential gearing having planets which mesh on the one hand with an internally toothed annular gear wheel and on the other hand with an externally toothed sun wheel, with all the gear wheels being disposed in one plane. The torques transmitted to the two driven shafts vary in magnitude. The locking effect is based on the fact that the epicyclic spur gears with the inner sun wheel work as geared pumps with the relative rotation of the two driven shafts, i.e., when cornering or if the gear wheels connected to the driven shafts fully rotate. At the same time the pressure medium, normally lubricating oil, inside the differential gearing and forced radially outwards, is engaged by the toothing of the epicyclic gears and is conveyed radially inwards. At the same time the planet carrier is constructed as a pump housing tightly enclosing the epicyclic gears and the inner sun wheel. The locking moment is produced by the build-up of hydrostatic pressure, which is built up by clearances between the toothing and the housing and by axial clearances. The tighter the planets fit in the confined housing, the higher the locking moment is. Consequently, the planets have the tendency to restrain the relative rotation between the inner and outer sun wheel.
The known spur gear differential has the property that the input torque is distributed to the two driven shafts only in proportion to the radii of the inner and outer sun wheel respectively. It is not possible to distribute the torque equally to the two driven shafts. With a locking differential of the type described, the locking moment is distributed in the same ratio as the drive torque in the locking situation where there is a force-locking design.
For drives in which an equal torque is required for both driven shafts, differential gears are known from the text book "Zahnradgetriebe" (Johannes Looman, Konstruktionsbucher Vol. 16, Springer-Verlag) Pages 218-219. For bevel gear differentials as shown in FIG. 7.20, which are used especially between the two gear wheels of a drive axle, there are also known locking mechanisms of the type with which the resultant axial force from the toothing is used to operate a friction brake. From German Patent Document No. 23 00 343 there is also known a locking mechanism with which the two driven shafts are connected to the two halves of a viscous clutch, so that there is a permanent frictional connection between the two driven shafts.
Mechanical form-locking and externally controlled hydraulic locking mechanisms are too expensive and unreliable, especially for heavy vehicles. Furthermore, viscous locking mechanisms occupy a too great space.